The invention relates to motor vehicles in general, and more particularly to improvements in power trains of motor vehicles. Still more particularly, the invention relates to power trains of the type wherein a prime mover (such as an internal combustion engine) can transmit torque to an automated torque transmitting system (such as a friction clutch) which, in turn, can transmit torque to the input element of a transmission system shiftable (manually or automatically) into a plurality of gears. A power train of such character further comprises means for operating the automated torque transmitting system, preferably a signal-receiving and signal-transmitting control unit and actuating means for changing the condition of the torque transmitting system (such as the extent of engagement of a friction clutch) in response to signals from the control unit. The control unit can receive signals from monitoring means including one or more sensors, electric circuits and/or other signal generating and signal transmitting means, and such control unit can embody means for ascertaining the torque (Mmot) of the prime mover and an arrangement serving to compare rises and drops of torque (Mk) being transmitted by the automated system with rises and drops of the torque being transmitted by the prime mover.
Power trains of the above outlined character are disclosed, for example, in published German patent applications Serial Nos. 40 11 850, 44 26 260 and 195 04 847 to which reference may be had, if necessary. The disclosures of all U.S. patents and allowed U.S. patent applications specifically mentioned in this specification as well as of those corresponding to any and all foreign patents and patent applications identified in this specification are incorporated herein by reference.
Power trains of the type disclosed in the aforementioned German patent applications normally comprise a prime mover (such as an internal combustion engine or a hybrid system with a combustion engine and energy storing means and/or an electric motor). The prime mover can transmit torque to the input element of an automated torque transmitting system which can transmit torque to a manually or automatically shiftable transmission system. The condition of the torque transmitting system (such as a friction clutch) can be regulated or controlled by operating means including a control unit and actuating means (also called actuator) serving to directly or indirectly adjust the automated torque transmitting system, i.e., the latter can be caused to assume a fully engaged or a fully disengaged condition or any one of a plurality (e.g., an infinite number) of partly engaged conditions. The output element of the automated torque transmitting system can transmit torque to a transmission in the form of a manually shiftable multistage reduction gear or of an automated transmission cooperating with one or more actuator serving to automatically select and/or shift the automated transmission into a particular gear. The transmission system can operate with or without interruption of tractive power or force.
If a vehicle embodying a power train of the above outlined character is to perform a creeping or crawling movement as a result of planned (intentional) engagement of the automated torque transmitting system, the resulting movement is rather unpredictable (such as jerky and/or too fast). As a rule, or at least in many instances, such crawling movement is carried out by selecting the torque of the automated torque transmitting system in accordance with a characteristic curve, and the unpredictabilty of the resulting crawling movement is attributable, for example, to a shift of the operating point of an automated torque transmitting system (such as a friction clutch), namely to a shift of the exact point or setting when the automatic torque transmitting system begins to transmit torque during adjustment from the fully disengaged condition toward the engaged condition.
If the engagement of an automated clutch, for the purpose of initiating a crawling or creeping movement of the motor vehicle, is realized by regulating the extent of adjustment of the clutch from its fully disengaged condition, namely by selecting a fixed value or extent of such adjustment, the crawling or creeping torque can vary as a function of several factors (such as the circumstances under which the motor vehicle is to perform a crawling movement) with the result that the rate at which the vehicle begins and proceeds to carry out a crawling movement can deviate from (by being faster or slower than) the desired or contemplated or customary rate.
On the other hand, it is highly desirable that the motor vehicle begin to crawl and to thereupon proceed with a crawling movement at a rate and in a manner as anticipated by the operator of the motor vehicle, i.e., the vehicle should be capable of carrying out a crawling movement which is as homogeneous and as predictable and comfortable (to the operator as well as to other occupant(s) of the vehicle) as possible. In other words, the operator as well as any other occupant(s) of the motor vehicle should be capable of expecting a predictable and at least substantially unchanging sensation whenever and as often as the vehicle is caused to perform a crawling movement. Thus, there exists an urgent need to enhance the ability of the power train in a motor vehicle to ensure a predictable and at least substantially unchanging smooth and comfortable initiation and carrying out of a crawling movement during the entire useful life of the vehicle.